[R] concatenating factor from list

[Sebastian Luque]

Hi,

I've run into a ridiculous problem I can't find any solutions for in the
archives or help pages:

data(barley)
cutYield <- with(barley, by(yield, variety, cut, breaks = c(0, 30, 60, 90)))

As in this example, I'm using 'by' to return a factor for each level of
another factor.  The problem is that 'by' returns a list of the factors,
and I need all these factors concatenated.  No problem, I said:

unlist(cutYield)

which returns an 'integer' class object, so it's no longer a factor.  The
same happens with:

do.call(c, cutYield)

I could recreate the factor from the integer level codes returned above,
but this is not good because this means redoing the job already done by
the function called in 'by', making the code more prone to errors.

Thanks in advance for any pointers,

-- 
Sebastian